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Preterm Labor and Short Cervix

Topic Overview

During pregnancy, the
cervix is a closed and sealed tunnel between the
uterus and the vagina. Before or during labour and delivery, the cervix
stretches and flattens (effacement). At 24 weeks of pregnancy, the average
cervix is about 35 mm (1.4 in.) long.1

Using
ultrasound imaging, researchers have found that at the
end of the second trimester (about 24 weeks), the shorter a woman's cervical
length, the more likely she is to deliver preterm. (This type of cervical
measurement requires special training and experience to perform accurately.)
Cervical length of less than
25 mm (1 in.) before 35 weeks
is considered a reliable sign of increased preterm labour risk. However, most
women with a shortened cervix do go on to deliver at term.2

How useful is this information?

If you have preexisting risk factors for preterm labour, the
absence of a shortened cervix is a reassuring sign that
preterm labour is not imminent.

There is a lack of proven treatment options for preventing preterm
labour over a period of weeks. So, knowing that you have a shortened cervix and
increased preterm labour risk may not change the way your doctor treats your
pregnancy.2 If you learn that you are at high risk,
make sure that you know the symptoms of preterm labour and that you know what to
do if you have them.